With the increased recognition of the prodromal, premotor, and non-motor features of Parkinson’s disease (PD), as well as the expanding knowledge concerning the clinical heterogeneity of PD, an overlap with other parkinsonian disorders and growing appreciation of genetic etiologies, there is a need to re-define PD, taking into account clinical, syndromic, etiologic and pathogenic aspects of parkinsonism. This book should be of interest, not only to clinicians concerned with the care of those afflicted with PD and related neurodegenerative disorders, but also to clinical and basic science investigators pursuing answers to some of the many unanswered questions about the pathogenesis and treatment of this challenging group of disorders.